I'm not sure what the industry standard might be, or what is dictated
by whatever governing body, but my
 preference would be to fuse both supplies individually.   To me, it
makes sense to fuse each individually.
 This might help troubleshooting later somewhat by possibly telling you
which supply was drawing too much
 current, and therefore might tell you which circuits to concentrate on
if and when it happens.
 If this is a very high volume product, fusing each might add enough
cost that it might be deemed
 uneconomical.  If it is a low volume product, the cost won't be as
scrutinized.
 If it's a onesey - twosey product, the extra cost won't really be felt
at all.

 This is my take on your question. =20

 Regards,

 Jim

> -------- Original Message --------
> Subject: [EE] Fuses Required - 1 or 2?
> From: "Gordon Williams" <gwilliams@ncf.ca>
> Date: Thu, December 01, 2011 11:50 am
> To: "Microcontroller discussion list - Public." <piclist@MIT.EDU>
>=20
>=20
> Darn, caught again.  Tag added.
>=20
>=20
> > Hi,
> >
> > I'm going to be running a 48V (at 3W) boost converter and a 5V (at 5W)
> buck
> > converter off of a 12 V battery.
> >
> > Is it a good practice to have a fuse on both supplies' inputs or just 1
> for
> > the system?
> >
> > >From a bit of research my understanding is that I should use a slow bl=
ow
> > fuse to handle the inrush current into the converters and I should size
> the
> > fuse at 150% the nominal rate.  Is that in the right ball park?
> >
> > Gordon Williams
> >
> > --=20
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> --=20
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